This invention relates, in general, to semiconductor devices, and more particularly to a method for cleaning semiconductor wafers prior to metal deposition by using a reactive sputter etch.
Semiconductor devices are manufactured on a substrate which is usually made from silicon. The silicon substrate is formed as a wafer, which is subdivided into chips. The chips are usually square or rectangular into which a specific electrical circuit has been fabricated. Each chip may have a single component or a combination and/or a multitude of components. Some examples of the components used are diodes, resistors, capacitors and transistors.
To fabricate the foregoing components requires various process steps, one of which is the deposition of a metal interconnect over the passive and active devices. To provide a good ohmic to metal contact requires that the surface of the devices be cleaned prior to the metal deposition. This is commonly called a metal preclean.
The fabrication steps of a field-effect transistor (F.E.T.) in a self-aligned silicide process are a good example of what can be found in the prior art for a clean prior to metal deposition. Through masking, etching and implanting techniques known in the art, the silicon substrate undergoes a variety of process procedures prior to the formation of the gate and source/drain regions. The gate is formed out of polysilicon and is isolated from below by a thin layer of oxide. The source and drain regions are formed by using photoresist and gate as a mask and implanting dopants into the substrate. Once the source/drain and gate regions are formed, a blanket film of oxide is deposited. This oxide is anisotropically etched by well known means such as using a reactive ion etcher (R.I.E ). Because of the directional nature of the etch all the oxide is removed except for the oxide on the sides of the gate. This "sidewall" oxide is necessary to prevent the gate to source/drain shorting during silicide formation. The thickness of the sidewall oxide also affects the device performance. To form metal contact regions, a metal is sputter deposited over the source/drain and gate regions. In this example, a low contact resistance is desired so the metal deposited is platinum which will later be annealed to form platinum silicide.
Prior to the platinum sputter deposition, a hydrofluoric acid dip and argon sputter etch is provided to remove any residual oxide or native oxide from the source/drain and gate regions. If the oxide is not removed from these areas, a platinum silicide will not form. Moreover, if the devices are placed in the hydrofluoric acid dip for extended periods of time the sidewall oxide will be etched away. In both cases the devices would be rejected. In addition, to use the argon sputter etch by itself would take a considerable length of time, thus being impractical.
Therefore, the foregoing process was found to have problems in the use of a hydrofluoric acid dip and argon sputter etch prior to the sputter deposition of a metal.